In the UL that would not work. You still need the modem in bridge mode and ClearOS connects to it with PPPoE. It has one RJ45 socket for the Ethernet connection to ClearOS and one RJ11 socket for connection to the phone line. Are you sure your phone line can take a direct ethernet connection. I would be surprised if a NIC could directly connect to it as the signalling and voltage standards are so massively different.
I think what is being suggested here is to set up a VLAN on the external NIC and give it a VLAN tag of 7, the configure it as PPPoE. Does it not work doing that?